1. Field of the Invention
The present invention relates to an improvement in endurance performance of a valve regulated type lead-acid battery using a Pb--Ca type alloy as a positive electrode grid.
2. Description of the Related Art
There are some types of valve regulated type storage batteries which are a starved type battery with a fine glass mat separator abutting on positive and negative plates and being currently most widely used; a gel type battery having an electrolyte gelled with colloidal silica which has been used from long ago in Europe and its vicinity; and a recently developed granular silica type battery in which granular silica is filled between and in the surroundings of the electrode plates, and the silica is impregnated with an electrolyte.
It is known that a Pb--Ca type alloy grid is used in these valve regulated type batteries as a positive electrode and, accordingly, the cycle life of these batteries is considerably shorter than that of conventional flood type batteries using an Sb alloy grid as a positive electrode. One of the causes of this is the deteriorate (softening) of the positive active material.
In order to solve the above problem, the following countermeasures in which a fine amount of antimony is added to the positive active material have been known.
(1) Unexamined Japanese Patent Publication (kokai) No. Sho-54-114729 discloses to add 0.05% or less of Sb.sub.2 O.sub.3 to a positive active material.
(2) Unexamined Japanese Patent Publication (kokai) No. Sho-56-82748 discloses that a positive plate uses lead powder produced from lead alloy containing Sb in the range of from 0.05% to 0.5%.
(3) Unexamined Japanese Patent Publication (kokai) No. Sho-58-209865 discloses to immerse a positive plate in an Sb.sub.2 O.sub.3 solution or blow Sb.sub.2 O.sub.3 to a positive plate.
(4) Unexamined Japanese Patent Publication (kokai) No. Sho-61-142666 disclose to add Sb.sub.2 O.sub.3 to a positive active material of a battery using a calcium grid.
(5) Unexamined Japanese Patent Publication (kokai) No. Sho-61-126551 discloses to add Sb.sub.2 O.sub.3 to a positive active material of a battery using a low Sb grid.
(6) Unexamined Japanese Patent Publication (kokai) No. Hei-1-200558 discloses to add antimony powder and silica powder in a range of from 0.05% to 0.5% to a positive active material of a valve regulated type battery.
(7) Unexamined Japanese Patent Publication (kokai) No. Hei-3-276561 discloses to add antimony or antimony oxide in a range of from 0.05% to 1%.
In spite of existence of such techniques, when the aforementioned antimony or antimony oxide is added actually, there are some cases where performance is improved and some cases where endurance is worsened instead of improved. As a result of examination of the cause for this, it was found that, in a battery having a capacity lowered in an early stage, antimony was precipitated on a negative plate to lower the charging efficiency and a large amount of sulfuric acid was accumulated. Further, when the result of the examination was studied statistically, the above phenomenon was observed mostly in a positive plate which was low in density of the active material. Further, as a result of various experiments, it was found that when antimony and arsenic were added at the same time, more remarkable improvement of endurance performance could be achieved by addition of antimony by a relatively small amount to an extent that the antimony had no influence on a negative plate. It was further found that not only addition of antimony to the paste but also the state as to whether the dispersion of antimony in the active material was well or not was a key point. It was further found that this phenomenon occurred frequently when a general container formation method (a method in which plate formation is performed in a state in which electrode plates are disposed in a battery container), which is a general method for formation of a lead-acid battery at present, was used, and that this phenomenon occurred when the leaving time from electrolyte filling to start of formation was long. Because this container formation method is indispensable for cost reduction of the battery, it is essential to perform an improvement with this method as a premise.